As electronic devices bus widths and bus speeds increase, the components that drive those busses must accommodate the accompanying current surges through the power (VDD) and ground (VSS) connections of the components. The current surge flowing through the impedance in component power connections, results in a voltage oscillation between the component power or ground reference level and the “system” power or ground voltage reference level. Some common names for this voltage oscillation include “Ground Bounce”, “VDD Bounce”, and “Simultaneous Switching Noise” (SSI). These bounces may upset the circuitry and/or cause it to not operate properly. This may present a problem.
Measuring ground bounce or simultaneous switching noise on a component is done in a controlled lab bench environment. The test may be performed several ways, however it usually involves forcing one un-terminated output to a logic low state and attaching an oscilloscope between this output and the ground reference level in the system. The output should provide a low impedance path to the internal ground level (e.g. die ground in an IC (integrated circuit)), and the setup will allow an observation of any fluctuation in the voltage of the die ground relative to the system ground. While in this setup, as many other outputs as practical are forced to simultaneously switch from a logic high state to a low logic state. The fluctuation in the die voltage or “bounce” is observed on the oscilloscope. The bench environment may not represent the actual system usage of a component, resulting in false or incomplete results. This may present a problem.
Measuring VDD bounce is performed in a similar way, except the un-terminated output is forced to a logic high, and the remaining outputs are forced to switch from a logic low to a logic high. The bench environment may not represent the actual system usage of a component, resulting in false or incomplete results. This may present a problem.